Biochemically well-defined platelet plasma and granule membranes will be isolated by the refinement of current and recently-introduced techniques for fractionating platelets. Fractionating platelets by the method of Marcus et al. and by the method of Barber and Jamieson will be used to prepare platelet plasma membranes. The methods of Broekman et al. and that of Marcus et al. will be used to produce 'undamaged' granules. These granules will be separated and processed to prepare biochemically well-defined granule membranes. The purity and integrity of the platelet fractions will be checked by electronmicroscopy and currently used biochemical markers. The study will develop the means for identifying and differentiating the plasma and granule membranes. The plasma membrane will be labeled in the intact platelet. After the platelet is disrupted and the fractions isolated, the label will serve as a plasma membrane marker. Non-penetrating agents such as galactose oxidase and H3-trinitrobenzene-sulfonate as well as enzymatic iodination using immobilized lactoperoxidase will be used to label the platelet surface. Platelet enzymes that are membrane-bound and potentially can serve as reliable plasma membrane markers will be identified. Particular attention will be directed to evaluate platelet adenyl cyclase as a platelet plasma membrane marker. BIBLIOGRAPHIC REFERENCES: Shick, P.K., K.B. Kurica, and G.K. Chacko. Location of Phosphatidylethanolamine and Phosphatidylserine in the Human Platelet Plasma Membrane. J. Clin. Invest. In Press, May 1976.